#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 40
char *s_gets(char *st, int n);
struct book
{
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int main()
{
    struct book library[MAXBKS];
    int count = 0;
    int index, filecount;
    FILE *pbooks;
    int size = sizeof(struct book);
    if ((pbooks = fopen("book.dat", "a+b")) == NULL)
    {
        fputs("Can't open book.dat file\n", stderr);
        exit(1);
    }
    rewind(pbooks);
    while (count < MAXBKS && fread(&library[count], size, 1, pbooks) == 1)
    {
        if (count == 0)
        {
            puts("Current contents of book.dat: ");
            printf("%s by %s: $%.2f\n", library[count].title, library[count].author, library[count].value);
            count++;
        }
    }
    filecount = count;
    if (count == MAXBKS)
    {
        fputs("The book.date file is full.", stderr);
        exit(2);
    }
    puts("Please add new book titles.");
    puts("Press [enter] at the start of a line to stop.");
    while (count < MAXBKS && s_gets(library[count].title, MAXTITL) != NULL && library[count].title[0] != '\0')
    {
        puts("Now enter the author.");
        s_gets(library[count].author, MAXAUTL);
        puts("Now enter the value.");
        scanf("%f", &library[count++].value);
        while (getchar() != '\n')
        {
            continue;
        }
        if (count < MAXBKS)
        {
            puts("Enter the next title.");
        }
    }
    if (count > 0)
    {
        puts("Here is the list of your books: ");
        for (index = 0; index < count; index++)
        {
            printf("%s by %s: $%.2f\n", library[index].title, library[index].author, library[index].value);
            fwrite(&library[filecount], size, count - filecount, pbooks);
        }
    }
    else
        puts("No books? Too bad.\n");
    puts("Bye.\n");
    fclose(pbooks);
    return 0;
}
char *s_gets(char *st, int n)
{
    char *ret_val;
    char *find;
    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        find = strchr(st, '\n');
        if (find)
        {
            *find = '\0';
        }
        else
            while (getchar() != '\n')
            {
                continue;
            }
    }
    return ret_val;
}